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    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
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    <!-- 返回数组的所有子集 -->
    <script>
      var subsets = function (nums) {
        let res = []
        // 记录走过的路径;
        let track = []
        const backtrack = (nums, start, track) => {
          res.push([...track])
          // 注意 i 从 start 开始递增
          for (let i = start; i < nums.length; i++) {
            // 做选择
            track.push(nums[i])
            // 回溯 基于选这个数，继续递归，传入的是i+1，不是start+1
            backtrack(nums, i + 1, track)
            // 撤销选择
            track.pop()
          }
        }
        backtrack(nums, 0, track)
        return res
      }
      console.log(subsets([1, 2, 3]))
    </script>
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